While mast cells are normally present in the skin in small numbers in a perivascular pattern, in mast cell diseases an increased number of mast cells is present. In telangiectasia macularis eruptiva perstans, the increase in mast cell numbers is small. Their nuclei are typically spindle-shaped, and they are concentrated around blood vessels. Often they resemble fibroblasts, therefore special stains are needed to identify the mast cells.
Within the dermis, there is a perivascular and interstitial infiltrate of mononuclear cells. Abundant cells containing round, oval or spindled nuclei with ample cytoplasm are present within this infiltrate. Their cytoplasm is characterized by the presence of metachromatic granules, highlighted upon staining with Giemsa, toluidine blue or Leder stains.